Reinforced concrete is a popular construction material. It typically uses embedded reinforcement structures that have high tensile strength and ductility to reinforce concrete.
One popular type of reinforcement is a steel reinforcement bar (i.e, rebar). A rebar may be a hot-rolled or cold-drawn metal rod with circular cross section and ribbed surface. The ribs of various shapes enhance bonding between the rebar and concrete for joint performance under tension and flexion or bending. However, due to small height of the ribs, the bonding between the ribs and concrete can break under the stress, causing slippage of the rebar inside concrete, which weakens the concrete. To obtain the necessary tensile strength of the reinforcement, the amount of rebar must be increased, which adversely increases weight of the reinforcement and cost of construction of the reinforced concrete.
Another popular type of reinforcement may be manufactured from tubular blanks with hot-rolled corrugated ribs. This manufacturing method provides a reduced weight of the reinforcement. However, such a tubular reinforcement structure typically cannot be made with a diameter less than 20 mm. Furthermore, the economic gain is insignificant, due to the increased complexity and energy consumption in the manufacturing of such reinforcement.
Another type of reinforcement is a cable reinforcement, which includes several metal wires wound into strands. This type of reinforcement structure provides a more effective reinforcement than the rebar, but has much higher cost of manufacture.
The main drawback of all these kinds of reinforcement is the ineffective use of the material: under combined loading of a reinforced concrete structure, such as under combined bending and tension, only the surface layers of the reinforcement are in fact working. The strength properties of the structure are not fully utilized.
In the past century, a substantial number of efforts have been made to develop spiral reinforcements whose structural quality coefficient (load-bearing capacity per mass) is substantially higher than that of the ribbed rebar currently being used.
One known rebar design is a steel band of rectangular cross-section twisted into a spiral, whose ribs after twisting are subjected to a deformation pattern. This technical solution also does not optimize the use of the material in the reinforcement structure.
Thus, there is a need for an improved reinforcement for reinforced concrete, which has lower weight while fully utilizing the strength properties of its material.